As far as I can remember, pennant has not been awful at all.. in fact my general impression (possibly inaccurate i know) is that he has done alright whenever he got his chance. But I guess the same can be said about bellamy, crouch, finnan, etc before they left.. weren't bad but weren't outstanding either.
We will just never be able to fully understand what Rafa sees or doesn't see in a player.
But the pattern is pretty similar so far.. First he bought someone, then he tried him, then he shelved him and eventually sold him. Sometimes real quick (Pellegrino, morientes) and often without proper explanation. But so be it cos he is the boss and we must assume he sees more than what we can see on the surface.
I would say pennant (& possibly babel) is currently falling into this category. And while you are in it, it has almost certainly marked the end of your liverpool career. Crouch is obviously the prime example.